Said wrenches are used, for example, in the automotive field, especially in manufacturing plants but also in repair shops. In practice, manual devices are designated manual wrenches even though said devices are motor-driven. Said devices are designated hereafter as rod-type wrenches when they have a rod-shaped housing; they are designated pistol-type wrenches when their housing is of an offset design.
The drive means is usually electricity or compressed air. With electric devices, the motors are usually supplied with electric power from a central source via a connecting cord, or in a decentralized manner from a storage battery; however, wrenches with other types of power supply, e.g. battery, capacitor, or other electrical storage means are conceivable.
Based on a possibly existing pneumatic or electrical power connection, said wrench then has an actuating grip, then a motor and gear means connected to it, usually a planetary gear means, and connected to said gear means a clutch to which the freely terminating end section of the wrench designated the “head” is attached, said head conceivably being designed as straight or—especially with rod-type wrenches—as an angle head. In practice, said rod-type wrenches with angle heads are frequently no longer designated rod-type wrenches but “offset wrenches.” A head is designated an angle head when its drive shaft is offset relative to the output shaft, frequently at an angle of 90°. At the free end of the head, the output shaft is usually designed square so that attaching sockets with the desired wrench size for driving may be attached.
In practice, it has proven advantageous to design said heads as separate components since they are the first component group of the wrench to wear out, especially when they are designed as angle heads, making fast and inexpensive repairs to the wrench feasible simply by replacing the head. Additionally, said replaceable heads offer the advantage of arranging various head designs attaching to the actual base unit of the wrench so as to ensure optimum accessibility of the screwing location.
Safety-relevant screwing locations, e.g. in the area of the steering or brake systems, are usually implemented in a two-step tightening process: First a driving operation of approximately 80% to 90% of the target tightening torque is performed as quickly as possible, followed by a relatively slow further tightening of the bolt. The load release between these two steps during tightening takes into account the settling behavior of the screwing location and ensures especially reliable adherence to the desired target or nominal torque from the tightening torque actually achieved during the driving operation.
The initial fast tightening during said two-step driving operation is usually performed by motor by means of said manual wrench. The end of this motorized initial tightening of the bolt is reached by a torque limiter which is either directly incorporated into the manual wrench, or, in the case of pneumatic so-called “choke-type” wrenches, the maximum torque to be applied can be limited by the air pressure with which the tool is driven so that here the torque limiter attached to the drive motor is implemented outside the actual tool.
Subsequently, the worker must use a second device, i.e. a hand-actuated torque wrench, since the motorized manual wrench cannot ensure the required precision needed to maintain the tightening torque. The torque wrench has the required precision so that, within the range of specified tolerances, the torque wrench releases precisely at the preset nominal torque, for example, by means of an articulated mechanism, such that a clearly audible clicking and a certain amount of backlash of the torque wrench is generated which indicates that the correct tightening torque has been obtained. From practical use, torque wrenches are known which are adjustable or which release at the torque permanently preset at the factory. DE AS 21 06 263 also shows a torque wrench designed as an articulated wrench.
A motor-driven, hand-held wrench is known from U.S. Pat. No. 4,060,137, which wrench has means for torque limitation and the possible automatic shutoff of the wrench when a preset torque is achieved. This principle of this wrench is based on the design of the pistol-type wrench, with the components known from a pistol-type wrench, however, forming almost exclusively the grip area of a considerably larger, roughly flatiron-shaped, large housing. Said wrench does not have a freely terminating “head” in the aforementioned sense; rather, connected to the drive unit are gear means which in turn lead to the grip and the connection for the compressed-air supply provided therein. There is no provision for operating the wrench without the motor drive. The release precision of the pneumatic torque limiter is possibly insufficient for many safety-related screwing locations.
From practical use, a manually operated torque wrench from the Tohnichi Company is also known to which a air motor is attached and which consequently is not designated by the manufacturer or the distributor of these tools as a motorized manual wrench but instead as a torque wrench (“torque wrench with air motor”). Said torque wrench first permits the motorized tightening of the screw connection, the otherwise unmodified torque wrench being subsequently employed in the usual known manner. The manipulation of this device is arduous since it has comparatively large dimensions due to the attached compressed-air motor and thus poor accessibility to restricted screwing locations. Manipulation is further impaired by the fact that the relatively high weight of the air motor lies outside the longitudinal axis of the torque wrench such that the user must constantly compensate for this eccentricity by a correspondingly tighter, tiring grip in order to avoid unwanted tilting motions of the tool around its longitudinal axis.
DE 25 20 250 A1 and DE 296 18 817 U1 each show a wrench with a torque limiter and ratchet drive, said devices being the only torque limiters provided on the wrench.
The object of the invention is to create a motor-driven manual wrench which allows for speedy work and the quick implementation of a driving operation, even with two-step tightening.